1. Field of the Invention
This invention relates to vibration dampening devices and particularly to electrically conductive vibration dampening devices.
2. Description of the Related Art
Electronic devices, including desktop computer systems, portable computer systems (e.g., laptop computers, notebook computers, sub-notebook computers, and palmtops), personal digital assistants, and cellular telephones, typically have sensitive, and/or costly components that must be protected from harmful mechanical vibration and shock. For example, in notebook computers, one of the most expensive and fragile components is the flat panel display, typically a thin-film transistor liquid crystal display (TFT-LCD). Because the computer is designed to be portable, and the typical notebook computer has a clam-shell design, i.e. the flat panel display is located in one half of the clam-shell and is attached to the other half of the clam-shell (which contains other computer system components) by a hinge, the flat panel display can be subjected to a variety of harmful mechanical vibrations and stresses.
Consequently, such devices are typically assembled with some manner of vibration dampener to help protect the sensitive components. In computer systems with flat panel displays, the display is often attached to the remainder of the system with the help of a dampening device such as a rubber grommet. Additionally, many sensitive components, particularly flat panel displays, must also be electrically coupled to the remainder of the system in order to provide adequate grounding or proper continuity among electromagnetic interference (EMI) shielding devices. This is particularly important for flat panel displays which often include high frequency driving circuitry.
Given the high cost and sensitivity of many system components, and the costs associated with assembling such devices, it is desirable to have low-cost, simple, and easy to assemble parts to simultaneously provide vibration dampening and electrical continuity where needed. An example of a prior art device can be found in U.S. Pat. No. 5,761,031, entitled "Conductive Shock Mount for Reduced Electromagnetic Interference in a Disk Drive System," which teaches a rubber shock mount grommet coated with a conductive material such as metallic paint or a flexible metallic coating. However, such a device has a number of drawbacks including high cost, high resistance, cracking, and flaking of the conductive coating when the device is subjected to compression, as is often the case for a vibration dampening device. Flaking of the conductive coating is particularly undesirable in electronic devices where the conductive flakes migrate (e.g. because of transporting a portable device) to other areas in the computer system and cause electrical shorts. Additionally, flaking of the conductive coating can reduce the grommets effectiveness as an electrical conductor. Another prior art solution involves using separate vibration dampening grommets and EMI clips to provide electrical continuity. However, such a solution requires additional parts and complicates assembly of a computer system.
Accordingly, it is desirable to have a simple vibration dampening device that is electrically conductive, low cost, low resistance, easy to manufacture and use, and without the aforementioned disadvantages.